1. Field of the Invention
This invention relates to the field of communications and more specifically to the field of antennas of the microstrip type.
2. Description of the Prior Art
Microstrip antennas generally have limited bandwidth, typically a few percent, and various approaches have been taken to increase the bandwidth of this type of antenna. For example, grated microstrip patches have been investigated in which the appearance of grating modes, in addition to the normal microstrip modes, has the effect of increasing the bandwidth.
U.S. Pat. No. 4,054,874, incorporated herein by reference, describes a mircostrip dipole antenna wherein a plurality of parallel dipole elements are capacitively coupled (i.e., electric field coupled) to a microstrip feed line. The patent suggests that the response of the dipole pair can be adjusted by varying the positions of the pair of dipoles relative to each other and relative to the microstrip line. While dipoles of equal length are preferred, the patent suggests that acceptable results were also obtained having dipoles of different lengths.
The publication INTERNATIONAL JOURNAL OF MICRO-WAVE AND MILLIMETER COMPUTER-AIDED ENGINEERING, Vol. 3, No. 2, at pages 143-150, describes a log periodic strip grating microstrip antenna having narrow patches that are coupled along nonradiating edges. A double layer geometry is provided, and the antenna is mounted above a through line, allowing electromagnetic coupling to all elements of the antenna.
The publication IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, Vol. 40, No. 11, November 1992 at pages 1367-1374 describes multifrequency operation of microstrip antennas having parallel dipoles of different lengths that are fed by a microstrip line through a rectangular slot that is cut in the ground plane. In this device, the radiating structure is always centered on the slot and formed of thin dipoles.
While devices of the above type have been generally useful for their limited intended purposes, the need remains in the art for a broadband quasi-microstrip antenna having a planar configuration, and comprising generally a tapered array of radiating/receiving elements that are transversely mounted in capacitively coupled relation to an elongated transmission line underlying the array, the dipole elements being mounted to form a planar, generally triangular-shaped pattern with relatively narrow spacing between the individual dipole elements, but with a relatively large spacing to width ratio.